As wind turbines spring up everywhere one must ask can the wind be harnessed efficiently? With the exception of wind power all kinetic energy comes from a source of potential energy. Kinetic energy from wind is fine if it is stored into a potential form until needed to be kinetic. Example: a windmill water pump can pump water out of a well into a trough for cattle to drink. While the wind dynamics vary wildly the thirst of the cattle determine the minimum amount of water that must be pumped to sustain their life. It matters not if the water drips or gushes out of the pump if the required amount of water is present in the trough when the cows come to drink. This is where the use of wind for electricity is problematic.
Electricity is the flow of electrons, electromotive force is what causes the electrons to move expressed as volts, amps is the number of electrons passing a point at a given time interval, direct current always flows in one direction in conductors and can be pulsating or constant, alternating current flows both directions in conductors, hertz is the time interval between changes of polarity in complete cycles. A typical hand drill requires 120 Volts 5 Amps 60 Hz; these are fixed requirements for the drill to operate without damage to the motor, gear drive and bit. Every thing that plugs into an outlet has its own electrical requirements.
The lazily turning wind farm turbines are abused internally by the slight and constant changes in wind velocity. First: the turbine hub is not full floating; the main shaft supports its weight with the bearings located in the nacelle rather than the bearings located inside the hub rotating around a fixed hollow spindle. This makes the hub exert a down and forward thrust when at rest or coasting and an up and rearward thrust under wind loading. Main shaft bearings cannot stay stationary for very long because of bearing damage from lack of an oil film and must be changed in about three years. Second: the gearbox is a multi-stage helical planetary design that increases the turbines 20RPM input to an output speed of 1200RPM or 1800RPM depending on whether the alternator has six rotor poles or four rotor poles. The helical cut on the gear teeth cause the gear sets to drive thrusting to one end of the ring gear and coasting to the opposite end of the ring gear. With the dynamic load that the wind exerts on the blades and hub the planetary gears hammer from end to end of the ring gear. Gearbox life is about five years if maintained properly. Third: a hydraulic pump and valve in the rotating hub pitches the blades via large bore long stroke hydraulic cylinders attached to each blade root. The Hydraulic tank is mounted in the nacelle and has a rotary coupler for the hub mounted hydraulics. The cylinder circuitry includes a parallel hydraulic accumulator for each blade cylinder. The accumulators absorb the torque in the blades when the wind surges strongly against them preventing hoses from rupturing while the hydraulic valve is closed, they also prevent excessive surges in electrical current that would affect the power grid and other wind turbines connected to it. The accumulators last about three months before needing a new diaphragm. This is because the rotation of the accumulator causes the oil in it to foam under the surging conditions perforating the diaphragm. Newer styles have piston type accumulators that last much longer but need more frequent nitrogen charges.
The wind turbines generate alternating current at 60 Hz (US) 600 Volts 1740 Amps maximum rating. The hertz and voltage outputs are fixed values that cannot change no matter what the wind does. The amperage output is the supposed free variable that links the wild dynamics of the wind to the power grid safely. Consider this, the speed when generating cannot change because that would change the fixed 60 Hz output. Sure if a direct current generator were used the speed could change but that would require brushes and a commutator that both wear out not to mention the need for an inverter to connect it to an alternating current grid. The need for a constant 600 volts requires that the cut in and cut out of actual generating be a narrow window of wind speed. Just because they are turning does not mean that the rotor poles are excited. The manufactures give generating velocities as low as 10MPH and as high as 40MPH wind speed but this is only if there is a natural gas turbine alternator near the wind farm to balance out the voltage surges that are apparent at these low and high wind speeds. The natural gas turbine alternator stations are needed because of the ability to throttle the output of the alternator IE: Potential (natural gas) to Kinetic (power grid AC electricity). The use of fossil fuel to balance the wind turbines output is hidden in the clever power generation term “Spinning Reserve”!
As I approach my 20th year as a mechanic I have to wonder where we are heading. I once had a 1973 Plymouth Satellite just to play with. I once lived in the city. I have learned a lot over the years about energy and its uses yet I am bombarded with “renewable energy” and “go green” when there is no renewable energy at all! Even the Sun does not reclaim the light and heat that its mass becomes as its nuclear reactions occur they even escape its gravitational pull and are forever gone!
— Bo Rogers, Mechanic, 4-5-2008
This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.
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